ABSTRACT Although infection with Mycobacterium tuberculosis (MTb) is the largest cause of death in HIV-infected individuals patients, the host immunological mechanisms that control susceptibility to TB infection and latent TB reactivation in both HIV-infected and uninfected individuals remain poorly understood. By interrogating host immunological responses in unique HIV+ Cambodian patients who successfully restricted latent TB reactivation and only developed clinical TB at extreme immunosuppression, we will test the hypothesis in Aim 1 that these patients possessed a limited, but potent, array of MTb-specific CD4+ T cell clones within their depleted CD4+ T cell compartment that expanded and allowed them to achieve TB cure and survival. We will also investigate T cell responses in a highly immunosuppressed HIV+ group of individuals who have no historical or immunological evidence of TB (TB-/HIV+) despite high TB exposure. In this case, we hypothesize that these patients either have IFN-?-independent T cell responses that control TB or that they are resistant to TB infection. Our preliminary studies demonstrate that the TB+/HIV+ patients exhibited significant expansion of CD4+ effector memory T cell (TEM) frequencies and significant contraction in CD4+ central memory T cell (TCM) frequencies following antiviral (ART) initiation within the first months post ART initiation as compared to the similarly immunocompromised patients without TB (TB-/HIV+). Furthermore, high throughput (HTS) T cell receptor (TCR) sequencing showed that the TCR repertoires of the TB+/HIV+ patients were significantly more clonal compared to the TB-/HIV+ patients. Moreover, within the group of TB+/HIV+ patients, those who experienced TB-associated immune reconstitution inflammatory syndrome (TB-IRIS) after TB/HIV treatment initiation, had an even more dramatic expansion of CD4+ TEM frequencies and significantly greater T cell clonal expansion compared to those TB+/HIV+ patients who did not experience TB-IRIS. Specifically, our studies in Aim 1 will elucidate TB antigen-specific multifunctional CD4+ and CD8+ T cells and indicate if IFN- ??independent T cell responses, such as CD40L+ co-stimulatory cells, CD107a+ T cells or MAIT cells are involved in the anti-TB response in these patients or the TB-HIV+ patients, and we will correlate these functional results with T cell clones in the patients' TCR repertoires. We will also examine the ability of the TB+/HIV+ vs. TB-/HIV+ individuals to restrict TB infection and growth of MTb in an in vitro TB infection model and correlate these results with the T cell findings. In Aim 2 we will test the hypothesis that humoral responses and antibody features and functional properties control TB restriction, resistance to infection, and TB-IRIS in these patients. We anticipate that these studies will lead to the discovery of new humoral and cellular correlates of immunity and the discovery of highly effective TCRs and immunogenic antigens that could be exploited in the TB vaccine design.